Background: Obesity is frequent in Mexico, but its importance for COVID-19 is still under debate. We aimed to describe its frequency in patients with severe COVID-19 in a referral hospital. Materials and methods: 167 patients hospitalized for suspicious or confirmed COVID-19, 66.7% male with a median age of 54 (interquartile range 43-63) were classified according to BMI and evaluated for comorbidities, coronavirus-2 polymerase chain reaction test results, and reason for discharge. Results: 75.3% of the patients were overweight or obese and 7.8% had grade III obesity. Increasing BMI related to higher probabilities of hyperglycemia (fasting glucose > 100 mg/dL, p = 0.044), but other comorbidities were similar among groups. The mortality rate among patients with Grade I obesity was 11%, whereas 33% of patients with either underweight or Grade III obesity died, depicting a U-shaped mortality curve. Conclusions: Obesity and its comorbidities are common in hospitalized patients in Mexico. Special efforts must be made to detect them, and further interventions to control the obesity pandemic will also be necessary to improve long-term results.